The usefulness of packet switching networks for the transmission of digital information, particularly bursty type information generated by computer equipment, has long been recognized. Such networks are generally point-to-point in nature, in that a packet from a single source is routed to a single destination by a routing address attached to the packet. The network responds to the routing address by connecting the packet to the destination identified by the address.
Increasingly, packet switching networks are being used to convey other types of data which has different switching requirements. For example, the commercial delivery of television requires that individual packets be routed to multiple network output ports. In a video delivery arrangement, efficiency can be achieved by using a broadcast physical address for each packet which address defines multiple destinations for the video packet. Broadcast physical addresses tend to be relatively long compared to other address types.
Prior packet networks which deliver multiple data types, such as point-to-point and broadcast, use a single address format for the routing of all packets. The address format is selected to provide some overall efficiency, given a projected mix of data types, but inefficiencies remain since a single address type is not optimum for both data types.
One prior packet network for connecting both broadcast and point-to-point packets, which is disclosed in J. S. Turner, U.S. Pat. No. 4,734,907, issued Mar. 29, 1988, connects all packets to a routing network via a copy arrangement. Packet copies of broadcast packets are made in the copy arrangement until as many copies exist as there are destinations for the packet. A separate point-to-point destination address is then affixed to each packet copy and the packet copies with their new packet addresses are applied to the routing network which connects them to the appropriate network output ports. Point-to-point packets traverse the duplicating arrangement without duplication and are connected to the routing network with a point-to-point address. A main problem with this arrangement is that a separate complex copy network must be provided so that all packets appear as point-to-point packets when applied to the routing network and inefficiencies are created by introducing multiple point-to-point packets to the routing network when a single broadcast packet could suffice.
Another mixed data type network is disclosed in M. N. Ransom et al., U.S. Pat. No. 4,701,906, issued Oct. 20, 1987. The Ransom arrangement affixes a broadcast address to each packet entering the routing network without regard to whether the packet is of the point-to-point or broadcast type. Use of the relatively long broadcast addresses on point-to-point packets consumes more network bandwidth than would be needed to deliver the point-to-point packets, introducing network inefficiencies.
A need exists in the art for a packet switching arrangement for multiple types of packets in which it is possible to use the most efficient packet address type with each packet type.